Dynamic carbon budgets and carbon debts for Aotearoa New Zealand and its building sector

• New Zealand's remaining carbon budgets will be exhausted within next 10 years • Building sector's carbon budgets reveal the urgency of decarbonisation in the sector • Dynamic carbon debts provide time-disaggregated targets for mitigation pathways • Upper and lower bounds for sharing methods support interpretation of results • Dynamic carbon budgeting supports time-differentiated building policies The remaining carbon budget (RCB) is a crucial parameter when setting climate budgets for nations and economic sectors that want to measure their progress in climate change mitigation. The Paris Agreement is the most widely used and accepted climate change mitigation target, and the global RCB specified by the Intergovernmental Panel for Climate Change (IPCC) provides the carbon budget remaining from the beginning of 2020 that can be emitted as CO 2 before the Paris Agreement’s target is exceeded. This research investigates the global RCB allocation to the national and building sector level in Aotearoa New Zealand, including consideration of different sharing approaches and modelling of potential future dynamic parameters for the RCB allocation, that are required to stay below 1.5°C warming between the years 2024 and 2050. The average national RCB ranges from 159 to 339 MtCO₂ from year 2024; based on an average annual emissions rate of 38 MtCO₂, it will be depleted in 4-8 years. Therefore, this study proposed a dynamic carbon debt framework that provides a more realistic representation of dynamic RCBs and the carbon debt over future years. Key findings include the urgency of timely interventions, the need for additional mitigation strategies beyond the current policy approach which is largely focused on increased plantation forestry, and the usefulness of time-disaggregated carbon budgeting to address exhaustion of the RCB. Overall, this study demonstrates the relevance of dynamic budgeting to guide effective climate policy at both the national and building sector levels.